Stage controller and exposure method in which position of the stage is controlled based on position measurements of first and second laser interferometers

ABSTRACT

An apparatus including a stage configured to be moved. A first laser interferometer measures a position of the stage in a first direction. A second laser interferometer measures a position of the stage in the first direction. A control unit (i) obtains a position of the stage based on an output of one of the first and second laser interferometers, (ii) controls a position of the stage based on the obtained position of the stage, (iii) performs switching of one of the first and second laser interferometers to the other of the first and second laser interferometers while the stage is moved at a constant velocity in the first direction, (iv) calculates a distance by which the stage is to be moved during a time interval, and (v) sets an initial value of the other of the first and second laser interferometers after the switching, based on a position measured by the one of the first and second laser interferometers at a start time of the time interval and the calculated distance.

This application is a continuation application of U.S. patentapplication Ser. No. 10/374,141, filed Feb. 27, 2003, now U.S. Pat. No.7,411,678.

This application also claims the benefit of Japanese Patent ApplicationNo. 2002-056419, filed Mar. 1, 2002, which is hereby incorporated byreference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to an alignment apparatus, a controlmethod thereof, an exposure apparatus, and a method of manufacturing asemiconductor device by an exposure apparatus controlled by the samecontrol method.

BACKGROUND OF THE INVENTION

Along with the development of today's information-oriented society, theintegration degree of a device, a circuit, and the like, has beenrapidly increasing in recent years. This is realized by the developmentof micropatterning techniques. For example, Japanese Patent Laid-OpenNo. 10-289943 discloses a system which controls a stage using a laserinterferometer. In this system, an interferometer, which measures theposition of the stage, generally has one measurement axis per one degreeof freedom of a movable shaft.

To increase the stroke of the stage in this system, the size of a mirrorfor an interferometer to be attached to the stage, however, needs to beincreased, thereby decreasing the dynamic characteristics of the controlsystem of the stage. Additionally, for example, if an interferometer isset in an exposure apparatus to perform measurement in a focusdirection, it is geometrically difficult due to the arrangementrelationship with a projection lens to arrange one optical axis, suchthat the entire movable range of the stage is measured while using theoptical axis of the interferometer.

Under these circumstances, in Japanese Patent Laid-Open No. 2000-187338,a plurality of laser interferometers are provided for one axis of thedriving stroke of the stage of an exposure apparatus, and switching isperformed between the interferometers in off-axis alignment measurementand in exposure, thereby attempting to reduce the weight of a mirror ofthe interferometer. To measure the position of a stage by switchingbetween two interferometers, a stroke is set within which the twointerferometers can simultaneously perform position measurement, and theposition measurement value of one interferometer, as the switchingtarget, is preset to the position measurement value of the otherinterferometer, which measures the position of the stage within thestroke. The same applies to a case wherein interferometer switching isperformed twice or more.

If switching is performed between a plurality of interferometers duringstage driving, an error of a certain magnitude proportional to themoving velocity occurs for a period of time during which the positionmeasurement value of one interferometer is read, and the positionmeasurement value of another interferometer is preset to the readposition measurement value. Variations in such periods of time cause anerror to have an indefinite magnitude, and the error magnitude of theheld current position accumulates. To avoid this problem, the number oftimes of interferometer switching in processing one wafer by an exposureapparatus is minimized, or interferometer switching is performed while awafer stage is stopped during baseline measurement.

However, an interferometer switching position needs to be arranged at aspecific position, such as a baseline measurement position limited bythe system. This results in system limits, and thus, for example,interferometer switching cannot be performed during stage driving.Additionally, indefinite times of switching (chattering), due tobackground vibrations of a stage, depending on the stop position, mayoccur.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of theabove-mentioned problems, and has as its object to provide, e.g., analignment apparatus and its control method which suppress errors causedby the switching of measuring devices during stage driving, an exposureapparatus, and a method of manufacturing a semiconductor device by anexposure apparatus controlled by the same control method.

According to the first aspect of the present invention, an alignmentapparatus, which drives to a target position a stage capable of movingat least in a two-dimensional direction, comprises a plurality ofposition measurement devices, which have a function of measuring aposition of the stage in one direction simultaneously from differentpositions, a switching device which switches from one of the pluralityof position measurement devices, which simultaneously measure theposition of the stage, to another, on the basis of at least one ofposition information and velocity information of the stage, and asetting device, which sets an initial value of a second positionmeasurement device after switching, on the basis of the position of thestage measured by a first position measurement device before switching,when the switching device switches between the position measurementdevices, wherein the switching device switches between the positionmeasurement devices during driving of the stage.

According to a preferred embodiment of the present invention, theapparatus further comprises a first computing unit, which calculates amoving velocity of the stage on the basis of a measurement result of theposition measurement devices, a time measurement device which measuresan execution time from when the first position measurement device,before switching, measures the position of the stage to when the initialvalue of the second position measurement device, after switching, isset, and a second computing unit, which calculates a product of themoving velocity calculated by the first computing device and theexecution time measured by the time measurement device, and the settingdevice sets, to the initial value of the second position measurementdevice, after switching, a value obtained by adding the product to theposition of the stage measured by the first position measurement devicebefore switching, when the switching device switches between theposition measurement devices.

According to a preferred embodiment of the present invention, theswitching device switches between the position measurement devices whenthe stage is moving at a constant velocity.

According to a preferred embodiment of the present invention, when aposition at which the stage moves at the constant velocity changes inaccordance with the target position, a switching position of theposition measurement devices is changed, such that switching between theposition measurement devices is performed at the position where thestage moves at the constant velocity.

According to a preferred embodiment of the present invention, at leastone of a driving acceleration and a driving velocity of the stage isadjusted to change a track and the target position, when the stage isdriven, such that switching between the position measurement devices isperformed at the position at which the stage moves at the constantvelocity.

According to a preferred embodiment of the present invention, theapparatus has a function of driving the stage to the target positionbefore a change.

According to a preferred embodiment of the present invention, theswitching device switches between the position measurement devices, tomeasure the position of the stage in the direction when the stage iskept stopped in the direction.

According to a preferred embodiment of the present invention, theposition measurement devices have a function of measuring the position,in a three-dimensional direction, of the stage capable of moving in thethree-dimensional direction.

According to the second aspect of the present invention, a method ofcontrolling an alignment apparatus, which drives to a target position astage capable of moving at least in a two-dimensional direction,comprises a measurement step of measuring a position of the stage in onedirection, simultaneously from different positions, using a plurality ofposition measurement devices, a switching step of switching from one ofthe plurality of position measurement devices to another, on the basisof at least one of position information and velocity information of thestage, and a setting step of setting an initial value of a secondposition measurement device, after switching, on the basis of theposition measured by a first position measurement device, beforeswitching, when in the switching step, switching between the positionmeasurement devices is performed, wherein, in the switching step,switching between the position measurement devices is performed duringdriving of the stage.

According to a preferred embodiment of the present invention, in theswitching step, switching between the position measurement devices isperformed when the stage is moving at a constant velocity.

The third aspect of the present invention is characterized in that analignment apparatus controlled by a control method of the presentinvention is used to transfer a pattern.

According to a preferred embodiment of the present invention, in theswitching step, switching between the position measurement devices isperformed after a lapse of a predetermined delay time or passage througha distance corresponding to the delay time immediately after passagethrough an area to be exposed.

According to the fourth aspect of the present invention, there isprovided a semiconductor device manufacturing method comprising acoating step of coating a substrate with a photosensitive material, anexposure step of transferring a pattern onto the substrate coated withthe photosensitive material in the coating step, using an exposureapparatus according to the present invention, and a development step ofdeveloping the photosensitive material of the substrate, on which thepattern is transferred in the exposure step.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a view showing an example of an alignment apparatus accordingto a preferred embodiment of the present invention;

FIG. 2 is a view of the alignment apparatus shown in FIG. 1, as seenfrom the side;

FIG. 3 is a graph showing the relationship between the Y-coordinate andinterferometers, whose measurement values are valid in the alignmentapparatus according to the preferred embodiment of the presentinvention;

FIG. 4 is a graph showing a method of inheriting the measurement valueof the current position in interferometer switching;

FIG. 5 is a view showing the trajectory of a wafer stage according tothe preferred embodiment of the present invention, and the switchingcoordinates of interferometers;

FIG. 6 shows timing charts of the stage driving velocity in thealignment apparatus according to the preferred embodiment of the presentinvention;

FIG. 7 is a diagram showing the arrangement of a control unit of thealignment apparatus according to the preferred embodiment of the presentinvention;

FIG. 8 is a graph showing the step driving waveform of the stage of thealignment apparatus according to the preferred embodiment of the presentinvention;

FIG. 9 is a view showing an example of an alignment apparatus accordingto another preferred embodiment of the present invention;

FIG. 10 is a view of the alignment apparatus shown in FIG. 9, as seenfrom the side;

FIG. 11 shows timing charts of the stage driving velocity of thealignment apparatus shown in FIG. 9;

FIG. 12 is a view showing the concept of an exposure apparatus used whenan alignment apparatus of the present invention is applied to asemiconductor device manufacturing process;

FIG. 13 is a flow chart showing the flow of the whole manufacturingprocess of a semiconductor device; and

FIG. 14 is a flow chart showing the detailed flow of the wafer process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

First Embodiment

FIG. 1 is a view showing an example of an alignment apparatus accordingto a preferred embodiment of the present invention, and particularly,shows a case wherein the alignment apparatus is applied to the waferstage of a semiconductor exposure apparatus. A Y mirror 5, an X mirror6, and a wafer chuck (not shown) are mounted on a wafer stage 7. Though,as the wafer stage 7, one capable of driving along the XYθ axes is shownin FIG. 1, for the sake of descriptive simplicity, one capable ofdriving along six axes may be employed. The X mirror 6 reflectsmeasurement light from an X-axis interferometer 3 or an X-axisinterferometer 4, and is used to measure the position coordinate, in theX-axis direction, of the wafer stage 7. The Y mirror 5 reflectsmeasurement light from a Y-axis interferometer 1 and a yawinginterferometer 2, and is used to measure the position coordinate, in theY-axis direction, of the wafer stage 7. A linear motor XLM 10 drives thewafer stage 7 in the X direction and is guided by an X-axis yaw guide 9.A linear motor YLM (stator) 11 drives a YLM (movable element) 12 in theY direction, and is guided by a Y-axis yaw guide 8. The wafer stage 7 isguided by a flat guide 13, and an interferometer to be used inmeasurement of the coordinate in the X-axis direction is switchedbetween the X-axis interferometers 3 and 4, depending on theY-coordinate value of the driven stage. More specifically, if the waferstage 7 is located near the Y-axis interferometer 1 of FIG. 1, the Xmirror 6 does not reach the optical axis of the X-axis interferometer 4,and thus, the X-axis interferometer 3 measures the X-axis position. Onthe other hand, if the wafer stage 7 is located far from the Y-axisinterferometer 1 of FIG. 1, the X-axis interferometer 4 measures theX-axis position for the same reason.

The main object of the present invention is to provide a means which canperform laser interferometer switching and inheritance of measurementvalues of the current position, with stability at high precision, whenlaser interferometers for two or more axes are arranged for one degreeof freedom of the wafer stage 7.

FIG. 2 is a view of the alignment apparatus shown in FIG. 1, as seenfrom the side. The position of the wafer stage 7 is measured by aninterferometer 204, which is fixed to a lens barrel surface plate 205.The interferometer 204 in FIG. 2 is one of the Y-axis interferometer 1,yawing interferometer 2, X-axis interferometer 3, and X-axisinterferometer 4, which are already described with reference to FIG. 1,as seen from the side. The lens barrel surface plate 205 is held by adamper 206 to float above a vibration damping base (pedestal) 203. Thelens barrel surface plate 205 is designed not to transfer high-frequencyvibrations from the floor to the interferometer 204 and an exposureapparatus projection optical system (not shown). A plurality ofinterferometers 204 are arranged on the lens barrel surface plate 205 atpositions in the Y direction and axial directions along whichmeasurement is to be performed. A stage surface plate 202 is designednot to transfer high-frequency vibrations from the floor to the waferstage 7, as with the lens barrel surface plate 205. A projection lens207 is mounted on the lens barrel surface plate 205 and it projects apattern image from a reticle 208, also mounted on the lens barrelsurface plate 205, onto a wafer (not shown) loaded on the wafer stage 7.

FIG. 3 is a graph showing the relationship between the measurement axesof interferometers whose measurement values are valid and theY-coordinate of the wafer stage 7 in the alignment apparatus accordingto the preferred embodiment of the present invention. If the wafer stage7 is located near the Y-axis interferometer 1 of FIG. 1, the measurementoptical axis of the X-axis interferometer 4 does not strike the X mirror6, and only the X-axis interferometer 3 measures the current position ofthe wafer stage 7 (zone A).

If the wafer stage 7 moves to near the center of the driving stroke,measurement light beams of both the X-axis interferometers 3 and 4strike the X mirror 6. Accordingly, both the X-axis interferometers 3and 4 can perform position measurement (zone B). If the wafer stage 7moves from the zone A to the zone B, the current position information tobe counted by the X-axis interferometer 4 has a value accumulating froman indefinite value, and thus, is worthless as a measurement valuerepresenting the current position of the wafer stage 7. For this reason,when the wafer stage 7 moves from the zone A to the zone B, ameasurement value is inherited from the X-axis interferometer 3 to theX-axis interferometer 4. For example, the X-axis interferometer 4 isforcibly set (preset) to have the current position information held bythe X-axis interferometer 3, and a relative movement amount of the waferstage 7 continues to be counted immediately after the inheritance. Thiscan obtain correct position measurement values all over the Y stroke ofthe wafer stage 7 using the X-axis interferometers 3 and 4. As aposition at which the measurement value of the current position isinherited from the X-axis interferometer 3 to the X-axis interferometer4, coordinates at which position measurement beams of both the X-axisinterferometer 3 to be inherited and the inheriting X-axisinterferometer 4 simultaneously strike the X mirror 6 must be selected.This also applied to a case wherein a measurement value is inheritedfrom the X-axis interferometer 4 to the X-axis interferometer 3.

If the wafer stage 7 is located far from the Y-axis interferometer 1 ofFIG. 1, the measurement optical axis of the X-axis interferometer 3 doesnot strike the X mirror 6, and only the X-axis interferometer 4 measuresthe current position of the wafer stage 7 (zone C). When the wafer stage7 moves from the zone C to the zone D, a measurement value is inheritedfrom the X-axis interferometer 4 to the X-axis interferometer 3 in thesame way.

Reference numerals Y1 and Y2 denote a switching position (Y1) where ameasurement value is inherited from the X-axis interferometer 3 to theX-axis interferometer 4 and a switching position (Y2) where ameasurement value is inherited from the X-axis interferometer 4 to theX-axis interferometer 3, respectively. Y1 and Y2 are preferably set atdifferent positions. This can avoid chattering (undesirable frequentswitching of an interferometer to hold a measurement value), which mayoccur when the target position of the wafer stage 7 is set to a positionin the vicinity of a switching position. If the alignment apparatusaccording to the preferred embodiment of the present invention is to beused for a scanning exposure apparatus, the switching positions Y1 andY2 may be changed in accordance with the step size in the X direction,such that an interferometer switching position does not appear duringscanning exposure in the Y-axis direction.

FIG. 4 is a graph showing a method of inheriting the measurement valueof the current position in interferometer switching. Stage coordinatesS0 to S4 represent an example of coordinates of interferometers forevery sampling time when the center of the wafer stage 7 moves from apoint A to a point B, as shown in FIG. 1. The target position of thewafer stage 7 is set such that, e.g., the wafer stage 7 moves across theswitching position Y1 shown in FIG. 3 at a constant velocity. The waferstage 7, having been moving toward switching position Y1 at a constantvelocity at the stage coordinates S0 and S1, approaches the switchingposition Y1 at the stage coordinate S2. The next stage coordinate S3 isobtained by S2−S1, or the stage moving velocity calculated usingpreviously sampled data (Vs) and sampling time interval (Ts).S3=S2+(S2−S1)  (1)orS3=S2+Vs*Ts  (2)

After an interferometer 1 (e.g., the X-axis interferometer 3) obtains ameasurement value at S2, an interferometer 2 (e.g., the X-axisinterferometer 4) is preset to have the value of S3 obtained by equation(1) or equation (2), at the next sampling timing. With this operation,the current position of the wafer stage 7 measured by the interferometer1 is inherited to the interferometer 2.

FIG. 5 is a view showing the trajectory of the wafer stage 7 accordingto the preferred embodiment of the present invention, and the switchingcoordinates of interferometers. Reference numerals 503 a to 503 c showthe layout of exposure shots arranged on the wafer. A reticle pattern istransferred onto the wafer, and the wafer is exposed to the patternthrough an exposure slit 505. The exposure slit 505 proceeds in parallelwith a scan axis (X) during exposure of an exposure shot (504 a). Whenthe exposure slit 505 passes through the exposure shot (504 b), it isimmediately stepped in the Y direction to reach the exposure startposition of the next shot (504 c). At this time, assume that theY-coordinate at which interferometer switching is performed is locatedat a coordinate of a dotted line 501 shown in FIG. 5. Sinceinterferometer switching is performed during acceleration in the Y-axisdirection, if the preset position of an interferometer as the switchingtarget is calculated by the method described with reference to FIG. 4,using equation (1) or (2), the magnitude of an error increases.

For this reason, in this case, the Y-coordinate at which interferometerswitching is performed is changed to a coordinate indicated by a solidline 502. With this operation, interferometer switching can be performedwhen an X stage is driven at a constant velocity. To obtain the sameeffect, a method of changing the maximum velocity so as to cause thewafer stage 7 to move at a constant velocity at an interferometerswitching position or changing the processing order of exposure shots tolengthen a Y-step distance may be employed. Alternatively, the waferstage 7 may be stepped to switch between interferometers, and thenstepped again to the original target position, such that a switchingpoint is located in a zone within which the wafer stage 7 moves at aconstant velocity. These methods, however, may decrease the flexibilityof the exposure processing sequence and the throughput. For this reason,these methods are preferably utilized as countermeasures against a casewherein a distance corresponding to the moving distance of aninterferometer switching point cannot be assured in a zone within whichat least two Y-axis interferometers are available (the zone B in FIG.3).

As described in the second preceding paragraph, since it is difficult toestimate the true position of the wafer stage during acceleration anddeceleration of the wafer stage, the magnitude of an error increases.More specifically, factors responsible for this include:

(1) present value calculation using an algorithm for creating the stagetarget track of a profiler 712 increases in complexity depending on thestep velocity and target value, and thus, function implementationbecomes difficult; and

(2) the stage has a deviation from the target value during accelerationand deceleration.

The problem (1) could be solved by employing a processor capable ofhigh-speed mathematical computations for control calculation andimproving a present processing algorithm in the future. As for theproblem (2), a follow-up deviation in acceleration can be suppressed toa critical level or less by changing the material or structure of thestage to decrease the weight. Therefore, interferometer switching whilethe stage is moving at a constant velocity, as described in the previousparagraph, is an example which can practically be implemented at thetime of the present invention. With an improvement in performance of aprocessor used for stage control and an improvement in stage structure,a switching function in various states, which include stageconstant-velocity movement, but are not limited thereto (e.g., duringstage acceleration or deceleration) can be implemented within the scopeof the present invention.

FIG. 6 shows timing charts of the stage driving velocity in thealignment apparatus according to the preferred embodiment of the presentinvention. Reference numerals 601 a and 601 b denote X-axis drivingprofiles when the exposure shots 503 a and 503 b, as shown in FIG. 5,are exposed, and 601 c, a Y-axis driving profile when the wafer stage 7is Y-stepped from the exposure shot 503 a to the exposure shot 503 b.Since the interferometer switching point 501 is located in anacceleration phase in the X-axis driving profile, the switching point isshifted to the interferometer switching point 502 located in aconstant-velocity phase. At this time, the X-axis driving profile 601 bmay be delayed and started after movement along the Y-axis ends, insteadof shifting the interferometer switching point 501. Alternatively, themaximum velocity of Y-stepping in interferometer switching may bedecreased to prolong a period of time for movement at a constantvelocity along X- and Y-axes, as indicated by 601 d. More specifically,upon completion of processing of the hatched portion of 601 a, whichrepresents a scanning exposure zone, stepping along the Y-axis isstarted for the next exposure operation. By decreasing the maximumvelocity in the Y-axis direction to shorten the time required foracceleration, a longer period of time for the transition to movement ata constant velocity along the Y-axis before the start of decelerationalong the X-axis as the scan axis can be assured. The same effect can beobtained by prolonging the settling time (a constant-velocity zone otherthan the hatched area of 601 a) during which X-axis scan is performed ifinterferometer switching occurs.

FIG. 7 is a diagram showing the arrangement of a control unit of thealignment apparatus according to the preferred embodiment of the presentinvention. A Y-axis laser interferometer counter 701, yawing-axis laserinterferometer counter 702, X-axis laser interferometer counter 703, andX-axis laser interferometer counter 704 separately count the measurementposition of the stage. A current position calculation unit 705 transmitspreset values 706 and 707 and preset trigger signals (not shown) to theX-axis laser interferometer counters 703 and 704, which performswitching in interferometer switching. A main controller 720 performsprocessing, such as calculation of the stage target position,designation of interferometer switching points, and the like. Theprofiler 712 generates, e.g., a profile, as shown in FIG. 8, in whichthe wafer stage 7 moves toward a target position 719, to reach it whileplotting an S-shaped trajectory. In FIG. 8, reference symbol ta denotesan acceleration start point, tc, a point at which driving at a constantvelocity is started after termination of the acceleration, td, adeceleration start point, and te, a stop point after termination of thedeceleration. The difference between a target value output 714 generatedby the profiler 712 and a current position 715 of the wafer stage 7 iscalculated by a difference computing unit 713. A deviation 716 obtainedby the difference computing unit 713 is converted to a manipulatedvariable of an actuator by a control compensator 717 and added to alinear motor driver 718.

Second Embodiment

FIG. 9 is a view showing an example of an alignment apparatus accordingto another preferred embodiment of the present invention, and,particularly, shows a case wherein the alignment apparatus is applied tothe wafer stage of a semiconductor exposure apparatus. The samereference numerals denote parts with the same functions as those in thefirst embodiment. The difference from the alignment apparatus of FIG. 1lies in that a plurality of interferometer axes are arranged withrespect to the X-axis in FIG. 1, while a plurality of interferometeraxes are arranged with respect to the Z-axis. The Y mirror 5 in FIG. 1corresponds to a YZ1 mirror 901 in FIG. 9, and the YZ1 mirror 901 isalso used as a bar mirror, which reflects measurement light of the firstZ-axis laser interferometer located in the Z-axis direction of FIG. 9.In addition, a Z2 mirror 902 is arranged on the opposite side of the YZ1mirror 901 to reflect measurement light of the second Z-axis laserinterferometer. Measurement light beams from the Z-axis laserinterferometers are introduced to optical pickups 903 a and 903 bthrough optical fibers (not shown). The measurement light beams emittedfrom the optical pickups 903 a and 903 b are reflected by cube mirrors904 a and 904 b in the Z-axis direction. A Z-axis optical system mount905 is fixed on an XLM 10. When a wafer stage 7 is driven along theY-axis, the Z-axis optical system mount 905 simultaneously moves in theY direction.

FIG. 10 is a view of the alignment apparatus shown in FIG. 9, as seenfrom the side. The Z-axis interferometer measurement light beamsreflected by the cube mirrors 904 a and 904 b in the Z-axis directionare deflected in a direction perpendicular to the incident direction bytriangular mirrors 906 a and 906 b to reach the YZ1 mirror 901 and Z2mirror 902. The triangular mirrors 906 a and 906 b are arranged at fixedpositions with respect to a projection lens 207, and a spot positionilluminated with measurement light moves in the Y-axis direction by theY-direction driving of the wafer stage 7. A triangular mirror 906 b isalso arranged at the back of the sheet surface and symmetrically withthe projection lens 207, and deflects interferometer measurement lightfor measuring the YZ1 mirror 901. In this embodiment, the projectionlens 207 needs to be arranged near the center of the stage drivingstroke. When a laser interferometer attempts to perform measurementalong the Z-axis, the measurement optical axis of the laserinterferometer, which perform the Z-axis measurement using theprojection lens 207, is blocked by the projection lens 207. Accordingly,interferometer switching must be performed within the driving stroke ofthe wafer stage 7. A method of switching between interferometers whilethe wafer stage 7 is in a stationary state has been proposed. Thismethod stops the wafer stage 7 over and over during exposure andalignment sequences, thereby decreasing the throughput of the apparatus.According to this embodiment, measurement axis switching of Z-axisinterferometers can be performed during driving of the wafer stage 7,and thus, a reduction in throughput caused by stationary switching ofinterferometer measurement axes can be avoided.

FIG. 11 shows timing charts of the stage driving velocity of thealignment apparatus shown in FIG. 9. When an exposure slit passesthrough an exposure zone corresponding to a hatched portion during ascan 601 a in the X direction, stepping in the Y and Z directions isstarted immediately. Assume that Y step (601 c) extends across a defaultinterferometer switching position 1101. In this case, a measurementvalue along the Z-axis is obtained by an interferometer Z2 in a regionon the left side of the interferometer switching position 1101 and isobtained by an interferometer Z1 in a region on the right side of theinterferometer Z1 in a region on the right side of the interferometerswitching position 1101. In the driving charts shown in FIG. 11,interferometer switching is performed during deceleration along theZ-axis. When a measurement value switching method using theinterferometers described with reference to FIG. 4 is to be employed,the magnitude of an error which may occur in inheritance of measurementvalues increases. For this reason, in the case of this arrangement, theinterferometer switching position is changed to a position 1102 to stopthe driving along the Z-axis. At the same time, the interferometermeasurement axis is switched from Z2 to Z1 at a timing at which Y-axisdriving is being performed at a constant velocity. For theinterferometer switching position, a position at which Y step (601 c)starts and the stroke vary, depending on the shot layout of a wafer tobe processed. Hence, the optimum interferometer switching position isdesirably changed to a value determined in consideration of theabove-described points of view in accordance with the step direction,step target value, and timing of stepping along the Z-axis. Since thedriving distance along the Z-axis is generally short in an exposureapparatus, stepping along the Z-axis terminates in a short time.Accordingly, if Z interferometer measurement axes need to be switched inY-stepping to the next shot (601 c), interferometer switching may beperformed at a predetermined delay period of time after the end of anexposure zone in 601 a.

As has been described above, according to the present invention, if aplurality of interferometers are provided for one axis, the operatingamount of a stage during a time when the second interferometer isforcibly preset to have the current position is held by the firstinterferometer. With this operation, errors which may occur in switchingmeasurement apparatuses during stage driving can be suppressed.Additionally, a position or timing at which the switching operation isperformed is changed in accordance with the driving pattern of thestage, and interferometer switching is performed during stage driving(e.g., when the stage is driven at a constant velocity), therebyobviating the need for the overhead time due to interferometer switchingand assuring the switching precision. This can obviate the need for aperiod of time required to switch between interferometers and suppresserrors, which may be caused by switching in an application such as anexposure apparatus.

Moreover, chattering, which may occur when the target position is set tobe near a switching position, can be avoided. This can minimize thenumber of times of interferometer switching and suppress accumulation oferrors in switching. In addition, the number of times of calibration foreliminating such cumulative errors can be reduced.

Other Embodiment

An embodiment in which an alignment apparatus according to the presentinvention is applied to an exposure apparatus used in the manufacturingprocess of a semiconductor device will be described next.

FIG. 12 is a view showing the concept of an exposure apparatus used whenan alignment apparatus of the present invention is applied to asemiconductor device manufacturing process.

An exposure apparatus 1200 according to a preferred embodiment of thepresent invention includes an illumination optical system 1201, areticle 1202, a projection optical system 1203, a substrate 1204, and astage 1205. The illumination optical system 1201 can employ, as exposurelight, e.g., ultraviolet rays which use an excimer laser, a fluorineexcimer laser, or the like, as a light source. Light emitted from theillumination optical system 1201 illuminates the reticle 1202. The lighthaving passed through the reticle 1202 is focused on the substrate 1204through the projection optical system 1203 to expose a photosensitivematerial applied on the substrate 1204. The substrate 1204 is moved to apredetermined position using the alignment apparatus according to thepresent invention.

FIG. 13 shows the flow of the whole manufacturing process of thesemiconductor device using the above-mentioned exposure apparatus. Instep 1 (circuit design), a semiconductor device circuit is designed. Instep 2 (mask formation), a mask having the designed circuit pattern isformed. In step 3 (wafer manufacture), a wafer is manufactured by usinga material such as silicon. In step 4 (wafer process), called apre-process, an actual circuit is formed on the wafer by lithographyusing the prepared mask and wafer. Step 5 (assembly), called apost-process, is the step of forming a semiconductor chip by using thewafer formed in step 4, and includes an assembly process (dicing andbonding) and a packaging process (chip encapsulation). In step 6(inspection), the semiconductor device manufactured in step 5 undergoesinspections, such as an operation confirmation test and a durabilitytest. After these steps, the semiconductor device is completed andshipped (step 7).

FIG. 14 shows the detailed flow of the above-mentioned wafer process. Instep 11 (oxidation), the wafer surface is oxidized. In step 12 (CVD), aninsulating film is formed on the wafer surface. In step 13 (electrodeformation), an electrode is formed on the wafer by vapor deposition. Instep 14 (ion implantation), ions are implanted in the wafer. In step 15(resist processing), a photosensitive agent is applied to the wafer. Instep 16 (exposure), the wafer is moved at high precision using theabove-mentioned exposure apparatus, and the circuit pattern istransferred onto the wafer. In step 17 (development), the exposed waferis developed. In step 18 (etching), the resist is etched except for thedeveloped resist image. In step 19 (resist removal), any unnecessaryresist after etching is removed. These steps are repeated to formmultiple circuit patterns on the wafer.

With the above-mentioned process, a wafer can be moved at a highprecision in the exposure step, and a circuit pattern can be transferredonto the wafer.

According to the present invention, an alignment apparatus and itscontrol method, which suppress errors caused by the switching ofmeasurement devices during stage driving, an exposure apparatus, and amethod of manufacturing a semiconductor device using an exposureapparatus controlled by the control method, can be provided.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the claims.

1. An apparatus comprising: a stage configured to be moved; a firstlaser interferometer configured to be used to measure a position of thestage in a first direction; a second laser interferometer configured tobe used to measure a position of the stage in the first direction; and acontrol unit configured (i) to obtain a position of the stage based onan output of one of the first and second laser interferometers, (ii) tocontrol a position of the stage based on the obtained position of thestage, (iii) to perform switching of one of the first and second laserinterferometers to the other of the first and second laserinterferometers while the stage is moved at a constant velocity in thefirst direction, (iv) to calculate a distance by which the stage is tobe moved during a time interval, and (v) to set an initial value of theother of the first and second laser interferometers after the switching,based on a position measured by the one of the first and second laserinterferometers at a start time of the time interval and the calculateddistance.
 2. An apparatus according to claim 1, wherein the control unitis configured to calculate the constant velocity using previous outputsof the one of the first and second laser interferometers, and tocalculate the distance by a product of the calculated constant velocityand the time interval.
 3. An apparatus according to claim 1, wherein thecontrol unit is configured to calculate, as the distance, a distance bywhich the stage has been moved during the time interval using previousoutputs of the one of the first and second laser interferometers.
 4. Anapparatus according to claim 1, further comprising a third laserinterferometer configured to be used to measure a position of the stagein a second direction orthogonal to the first direction, wherein thecontrol unit is configured to perform the switching based on theposition measured by the third laser interferometer.
 5. An apparatusaccording to claim 1, wherein the control unit is configured to performthe switching while the stage is moved at the constant velocity based ona preset profile of a change in a velocity of the stage.
 6. An apparatusaccording to claim 1, wherein the control unit is configured to preset aprofile of a change in a velocity of the stage so that the switching isperformed while the stage is moved at the constant velocity.
 7. Anapparatus according to claim 1, wherein the stage is configured to chucka substrate , and the apparatus is configured to perform exposure of ashot on the chucked substrate to a pattern of light.
 8. An apparatusaccording to claim 7, wherein the control unit is configured to performthe switching while the stage is moved at the constant velocity, withoutthe exposure of the shot.
 9. An apparatus according to claim 8, whereinthe control unit is configured to preset a profile of a change in avelocity of the stage, so that the switching is performed while thestage is moved at the constant velocity, without the exposure of theshot.
 10. A method of manufacturing a device, the method comprising: (a)exposing a shot on a substrate to a pattern of light using an apparatus;(b) developing the exposed substrate; and (c) processing the developedsubstrate to manufacture the device, wherein the apparatus comprises:(i) a stage configured to chuck the substrate and to be moved; (ii) afirst laser interferometer configured to be used to measure a positionof the stage in a first direction; (iii) a second laser interferometerconfigured to be used to measure a position of the stage in the firstdirection; and (iv) a control unit configured to obtain a position ofthe stage based on an output of the first and second laserinterferometers, to control a position of the stage based on theobtained position of the stage, to perform switching of one of the firstand second laser interferometers to the other of the first and secondlaser interferometers while the stage is moved at a constant velocity inthe first direction, to calculate a distance by which the stage is to bemoved during a time interval, and to set an initial value of the otherof the first and second laser interferometers after the switching, basedon a position measured by the one of the first and second laserinterferometers at a start time of the time interval and the calculateddistance.